It goes without saying that cancer is a feared and life-destroying disease. Countless resources and endless research have been directed toward the development of effective treatment of this disease.
Rather than use invasive methods such as surgery, it has been known to apply laser irradiation to destroy cancer cells residing on the internal surface of organs, such as human urinary bladders.
Prior developments in this field will be generally illustrated by reference to the following patents:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 4,470,407 H. M. G. Hussein 09/11/84 1,089,805 G. Wolf 03/10/14 4,693,556 J. S. McCaughan 09/15/87 4,676,231 H. Hisazumi et al. 06/30/87 4,313,431 F. Frank 02/02/82 4,612,938 R. Dietrich et al. 09/23/86 4,512,762 J. R. Spears 04/23/85 4,512,762 J. R. Spears 01/24/89 4,723,556 M. L. Sussman 02/09/88 ______________________________________
One method of treatment has been to attempt to direct laser light radiation only on the tumors. Hussein in U.S. Pat. No. 4,470,407 and Frank in U.S. Pat. No. 4,313,431 teach devices utilizing this method. Devices such as those of Hussein and Frank comprise endoscopic apparatus having optical viewers whereby the physician can look at the interior of the cavity and manipulate the position of the tip of a laser light transmitting fiber so that a relatively focused beam of radiation is directed toward the visible cancer tissue. This method does not teach positioning the tip of the laser fiber centrally within the cavity because it does not contemplate the uniform irradiation of the entire inner cavity surface at one time. One problem with this method is that it is effectively limited to the treatment of visible cancers.
On the other hand, photodynamic therapy is a relatively recently developed curative procedure whereby a dye-like photoactivating drug, such as a hemotoporphyrin derivative (HpD) is taken into tumors by oral administration or by injection. Laser irradiation of the entire interior of the diseased organ selectively destroys the tumors through a photochemical reaction, but could harm healthy tissue if it is not performed properly. Even microscopic cancers can be treated, since the radiation does not need to be focused away from healthy tissue because the healthy tissue contains relatively little of the photoactivating drug.
Successful treatment requires that the dosage be uniform. Over-irradiation of healthy tissue causes "hot spots" or burn regions in healthy tissue. Under-irradiation results in "cool spots" wherein there is less than complete necrosis of the cancerous tissue, which may then reappear at a later time.
McCaughan in U.S. Pat. No. 4,693,556, Hisazumi et al. in U.S. Pat. No. 4,676,231, and Dietrich et al. in U.S. Pat. No. 4,612,938 teach attempts to irradiate the entire cavity by adding light diffusing means somewhere between the laser fiber tip and the inner cavity wall. This approach recognizes that the light directed at the cavity wall must be uniform so that hot and cool spots will not occur at different areas of the wall. Dietrich et al. teach the use of a balloon catheter which is filled with a light scattering or dispersing medium for this purpose.
Hussein also teaches the use of a balloon catheter, in this case to displace opaque fluids away from the tumor viewing means. Spears, in U.S. Pat. No. 4,512,762, teaches a balloon catheter which expands to conform to the irregular surface of an artery affected by atherosclerosis. Spears also shows, in U.S. Pat. No. 4,799,479, a balloon catheter with an acoustic sensor for sensing the sounds produced by heating tissue. The acoustic sensor is located away from the balloon/tissue wall interface and is used to detect the presence or absence of plaque vaporization, rather than to measure sound quantity or quality.
This art only addresses the problem of disseminating spherically uniform radiation away from the laser fiber tip. These teachings do not solve the problem of ensuring that the cavity wall itself receives the radiation in a uniform manner. This requires that all of the irradiated tissue be located at essentially the same distance from the light source. In the prior art, this is usually roughly accomplished by attempting to position the laser fiber tip in the center of the cavity of the organ through use of external ultrasonic wave positioning apparatus as taught by Hisazumi. The balloon of Dietrich et al., being much smaller than the cavity, must be similarly positioned.
This solution is unsatisfactory because, first of all, the tip may move and have to be continually repositioned. More important, however, is the fact that an organ, such as a bladder (even when full), will not be of uniformly spherical shape. A laser diffuser tip which fortuitously might be positioned in the exact center of gravity of a non-spherical body still would not result in uniform irradiation, since parts of the cavity wall will be significantly farther away from the tip than others and, hence, receive a smaller dose. There is no known diffusing medium which will completely compensate for the non-uniform dosages which result from spatial disparities.
This problem is exacerbated by the fact that the intensity of radiation is inversely proportional to the square of the distance from its source. Even a slight asymmetry in the bladder's shape will result in unacceptably large differences in dosages and could cause a dangerous incidence of under-irradiated cool spots and over-irradiated hot spots.
Therefore, there exists a need to provide uniform illumination at the organ's surface during photodynamic therapy, which need has been unsatisfactorily addressed in the existing art through the emphasis in the art on uniformity only at the radiation source.